Assessment of bone mineralization in children and adolescents
ABSTRACT Bone mineral accrual during growth results in gender-, race-, and maturation-specific changes in trabecular and cortical density
and dimensions. Children with chronic disease have multiple potential risk factors for impaired bone accrual. Risk factors
include delayed growth and maturation, decreased weight-bearing activity, malnutrition, vitamin D deficiency, glucocorticoid
therapy, impaired sex hormones and growth hormone, and increased bone resorption by inflammatory cytokines. The impact of
chronic diseases may be immediate, resulting in childhood fragility fractures, or delayed, owing to suboptimal peak bone mass
accrual and increased fracture risk with the inevitable bone loss during aging. Dual energy X-ray absorptiometry is, by far,
the most frequent method for the assessment of bone health in children at risk. This assessment is hampered by lack of a agreement
on the quantitative definition of osteopenia and osteoporosis in children, inadequate reference data, technical limitations
in small children, and varied approaches to the interpretation of results in children with delayed growth and maturation.
This review summarizes the expected gains in bone size, mass and strength during childhood and adolescence, the role of the
bone—muscle unit, the advantages and disadvantages of the available technologies for the assessment of skeletal health in
children, and possible alternative strategies for the assessment of bone healthy in children with delayed growth and maturation.
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ABSTRACT: This article defines what is meant by glucocorticoid-induced bone loss (GIBL) in children, as opposed to glucocorticoid-induced osteoporosis. G1BL is found in various conditions, including therapy of chronic inflammatory states, antenatal and postnatal glucocorticoid administration to reduce respiratory distress syndrome risk, pre- and postorgram transplantation, and in certain malignancies. The prevalence of G1BL has not been determined for all conditions, but the published literature indicates a general occurrence rate between 25 and 33%. The effects of glucocorticoids on bone cells are discussed, including dimerization of the receptor, nuclear transport, and stimulation of nuclear transcription factors. Nongenomic actions are also mentioned. The glucocorticoid-induced apoptosis of osteoblasts and osteocytes and the reduction of marrow stromal cell differentiation into osteoblasts are mentioned, and it is postulated that osteocyte apoptosis may alter mechanical transduction and contribute to the creation of microdamage in the bone and an increase in fracture risk. Cushing’s disease is employed as a model of pure G1BL, whereas other conditions are more complex because additional factors may contribute to bone loss, such as the excessive monocytic production of pro-inflammatory cytokines in inflammatory conditions, and the use of cyclosporin A posttransplantation. Algorithms for the diagnosis and management of G1BL are provided, and consideration of the relative risk of inhaled steroids is also mentioned.Clinical Reviews in Bone and Mineral Metabolism 2(1):37-52.
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ABSTRACT: The aim of this thesis was to investigate some methods for quantitative analysis of bone structure, particularly techniques which might ultimately be applied post-operatively following orthopaedic reconstruction operations. Initially it was decided to explore the efficacy of MRI in quantifying the bone structure at high resolution by comparing high resolution MRI against 'gold standards' such as Scanning Electron Microscopy (SEM) and optical histology. This basic study provided a measure of the distortions in the morphological bone parameters derived from MR images due to susceptibility artefacts and partial volume effects. The study of bone architecture was then extended to a model of advanced renal osteodystrophy in a growing rat. For this study, high-resolution micro computed tomography (microCT) was used and as a result of the high resolution images obtained, three new bone morphological parameters were introduced to characterise the bone structure. The desire to study bone architecture post-operatively in hip replacements led to a preliminary study on ex-vivo sheep acetabulae following total hip replacement, to determine the extent that the bone architecture could be investigated around the acetabulum. The motivation for studying the acetabulum was based on the high occurrence of debonding at the bone / prosthesis interface. This study demonstrated the superior nature of 3D MRI over conventional x-ray radiographs in early quantitation of fibrous membranes located between the host bone and the non-metallic implant and/or the bone cement. The presence of such fibrous membranes is strongly indicative of failure of the prosthesis. When using clinical MRI to image post-operative hip replacement, the image quality is severely affected by the presence of the metallic implant. The head of the prosthesis is shaped like a metal sphere and is located in the acetabular cup. This problem was investigated by performing simulations of MR images in the presence of the field perturbation induced by the presence of a metal sphere, with the effects of slice excitation and frequency encoding incorporated into the simulations. The simulations were compared with experimental data obtained by imaging a phantom comprising a stainless steel ball bearing immersed in agarose gel. The simulations were used to predict the effects of changing imaging parameters that influence artefact size and also to show how current metal artefact reduction techniques such as view angle tilting (VAT) work and to identify their limitations. It was shown that 2D SE and VAT imaging techniques should not be used when metallic prosthesis are present due to extreme slice distortion, whereas 3D MRI provided a method that has no slice distortion, although the effects of using a frequency encoding gradient still remain.
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ABSTRACT: Dissertação (mestrado)—Universidade de Brasília, Faculdade de Ciências da Saúde, 2009. A aquisição de massa óssea das crianças é um determinante fundamental na prevenção de fraturas e osteoporose. Vários trabalhos mostram correlações entre densidades minerais ósseas e índices radiomorfométricos de mandíbula em adultos. O objetivo desta pesquisa foi verificar se essa correlação existe também em indivíduos em crescimento. Para isso foram avaliadas as densitometrias ósseas da coluna lombar e corpo total exceto cabeça e radiografias panorâmicas de 94 crianças saudáveis - 42 meninos e 52 meninas - e 35 crianças com diagnóstico de Osteogênese Imperfeita tipos I, III e IV - 16 meninos e 19 meninas - com idades entre 5 e 18 anos. Foram testados cinco índices radiomorfométricos de mandíbula: mandibular cortical, visual, mentual, antegoníaco e profundidade antegoníaca. Esse estudo mostrou correlação entre os índices visual, mentual e antegoníaco com as densidades minerais ósseas e com as idades ósseas nas crianças saudáveis. Crianças com diagnóstico de Osteogênese Imperfeita apresentaram, proporcionalmente, mais corticais classificadas como C3 e finas, e em média os índices mentual e antegoníaco tinham espessuras menores, mesmo nas crianças que já estavam em tratamento com o pamidronato. A maioria das crianças com diagnóstico densitométrico normal apresentava corticais classificadas como C1 e não finas. ________________________________________________________________________________ ABSTRACT Bone mass aquisition in childhood is an important factor in fractures and osteoporosis prevention. Many studies show correlations between bone mineral densities and mandibular radiomorphometric indices in adults. The objective of this research was to verify if such a correlation exists also in growing individuals. Spine and whole-body densitometries and panoramic radiographs of 94 healthy children - 42 boys and 52 girls - and of 35 children with diagnosis of Osteogenesis Imperfecta types I, III and IV - 16 boys and 19 girls - aged from 5 to 18 years were evaluated. Five mandibular radiomorphometric indices were tested: mandibular cortical index, visual estimation of cortical width, mentual and antegonial indices and antegonial depth. This study showed correlation between visual estimation of cortical width, mentual and antegonial indices with bone mineral densities and skeletal ages in healthy children. Children with diagnosis of Osteogenesis Imperfecta showed more corticals classified as C3 and thin, and mentual and antegonial indices were thinner than in healthy children, even in those who were already in pamidronate treatment. Most of the children with normal densitometric diagnosis had corticals classified as C1 and not-thin.